In testing within clinical laboratories to measure various chemical constituents of biological fluids obtained from patients, such as whole blood, blood serum, blood plasma, and the like, fully-automated clinical analyzers may be used to improve testing accuracy and cost per test.
Typically, an automated analyzer includes an automated aspirating and dispensing system 100, such as shown in FIG. 1, which is adapted to aspirate a liquid (e.g., a sample of biological liquid 108S or a reagent liquid 107R) from a container (sample container 108 or reagent container 107) and dispense the liquid into a reaction vessel 113 (e.g., a cuvette). The aspirating and dispensing system 100 typically includes a pipetting operation where probe 104 (otherwise referred to as a “pipette”) mounted to a robot, performs aspiration and dispensing functions so as to transfer the liquid to the reaction vessel 113.
During the aspiration operation, the robot may position the probe 104 above the container, and descend the probe 104 into the container until the probe 104 is partially immersed in the liquid. A pump is then activated to draw in (aspirate) a portion of the liquid from the container into the interior of the probe 104. The probe 104 is then ascended (retracted) from the container such that the liquid may be transferred to the reaction vessel for testing. During or after the aspiration, an aspiration pressure signal from a sensor 130 may be analyzed to determine any anomalies, i.e., check for the presence of a clog or the presence of air should there be insufficient liquid remaining to carry out the desired aspiration.
Conventional systems may be able to acceptably perform these checks for anomalies when relatively large liquid volumes are aspirated (e.g., 30 μL or greater). However, if the volume of the aspirated sample is relatively small, noise in the pressure signal may dominate and may be so large that it may obscure the information contained in the pressure signal. Accordingly, when the aspirated liquid volume is relatively small, it may become very difficult to robustly verify proper aspiration. Thus, there is a need for improvements in pressure sensing during aspiration, especially when the aspirated volume of the liquid is relatively small.